The present invention generally relates to the field of electronic device manufacturing. More specifically, the present invention relates to utilizing a multi-material heat spreader for enhancing thermal performance of integrated circuit (IC) packages.
As integrated circuit fabrication technology improves, manufacturers are able to integrate additional functionality onto a single silicon substrate. As the number of these functionalities increases, however, so does the number of components on a single chip. Additional components add additional signal switching, in turn, creating more heat.
Heat dissipation is one of the most important challenges facing the semiconductor industry today. It is expected that within a few years, processors may be consuming more than 1,000 Watts of power. Numerous techniques are currently utilized by chip manufacturers to reduce the affects of this problem.
One common way to flush out heat is utilization of heat sinks. Heat sinks are generally pieces of material (often metallic) that pull the generated heat away from a chip. As the heat generated increases, so do the costs associated with providing an adequate heat sink. Another solution is liquid cooling which can be extremely expensive and is generally used for very expensive computer systems (such as super computers).
Other techniques include utilizing software procedures to improve parallelism and slowing down a chip""s clock speed. Transmeta Corporation of Santa Clara, Calif., utilizes a software-based approach by replacing transistors with software instead of slowing down a processor. These techniques, however, add overhead for the software procedures invoked and are generally less desirable because of the potential complexity involved.
Another problem created by the additional heat is thermal expansion. Generally, a semiconductor package provides a device with electrical connection to the motherboard, heat dissipation, and mechanical and environmental protection. As part of the mechanical protection function, the package can provide a solution to thermal expansion issues between the semiconductor device and the motherboard, for example.
During normal operation, the semiconductor device is expected to survive a fairly wide range of temperature fluctuations. While undergoing these fluctuations, if the device expands and contracts at one rate while the package and/or board move at vastly different rates, a great deal of stress can be generated within the combined structure. These stresses can produce failures within the components themselves or at any of the interfaces between these components.
Present state-of-the-art in electronic packaging consists of two forms of chip packagingxe2x80x94lidded and lidless (or bare). In a lidded package, a lid serves as a cover for the chip to prevent structural damage and also serves as a mechanism for transferring load forces present above the package to the board. In a lidless design, a bare package force transfer can occur through the die itself and, hence, the magnitude of the force has to be relatively much smaller than the lidded designs to ensure structural integrity of the die.
As for thermal properties, however, use of a bare die has a clear advantage. Namely, in a lidless design the elimination of the lid (which is one of the thermal interfaces) results in a better thermal performance or lower thermal resistance, when compared with a lidded package. Such lower thermal resistance becomes a necessity with an ever-increasing total power dissipation of the electronic packages. To be able to compete thermally with a bare die configuration, lid material needs to have a high thermal conductivity. Often such a material also has a coefficient of thermal expansion (CTE) that is not compatible with the CTE""s of the die and substrate material. Making use of such a material may be impractical in certain situations due to a drastic reduction in the package integrity and/or reliability.
The present invention includes novel methods and apparatus to enhance thermal performance of IC packages. In an embodiment, an apparatus for enhancing a thermal match between portions of a semiconductor device is disclosed. The apparatus includes a die and a heat spreader. The heat spreader is in thermal contact with the die. The heat spreader has a center portion and a perimeter portion. The center portion and the parameter portions are structurally coupled to each other.
In another embodiment, the perimeter portion of the heat spreader is selected from material with a lower CTE than the material for the center portion of the heat spreader.
In yet another embodiment, the thermal contact between the heat spreader and the die is established through thermal contacts between the perimeter portion of the heat spreader and the die.